Fix MSLT and MSLD response for QWK packet filename in root directory

Reusing the variable 'str' here for multiple purposes meant the QWK packet
filename was overwritten by the owner name (the system's BBS-ID):

 ftp> mlsd
 229 Entering Extended Passive Mode (|||2001|)
 150 Opening ASCII mode data connection for MLSD.
 Type=file;Perm=r;UNIX.ownername=VERT; 00index
 Type=cdir;Perm=elc;UNIX.ownername=VERT; /
 Type=file;Perm=r;UNIX.ownername=VERT; VERT

That last file there should have been "VERT.qwk"